1. n. [Production Logging]

A device for measuring the internal diameter of a casing, tubing or open borehole using high-frequency acoustic signals. A transducer (in transmit mode) emits a high-frequency pulse that is reflected by the pipe or borehole wall back to the transducer (in receive mode). The diameter is determined from the time of flight of this echo and the fluid acoustic velocity. The transducer is rotated to produce a cross section of the borehole size and full-coverage images of the borehole wall. The measurement has high resolution and is used to detect deformations, the buildup of scale, or metal loss due to corrosion. The amplitude of the echo from the inner casing surface provides qualitative information on the state of the surface, such as rugosity or corrosion. Casing thickness may also be measured simultaneously, either by analysis of the casing resonance signal, or by detecting separately the echoes from the inner and outer casing surfaces.

See: acoustic velocity,  borehole televiewer,  casing-inspection log,  electromagnetic caliper,  multifinger caliper,  ultrasonic measurement